Re: Creating properties in Lua-only classes

Wow, I just realized I was overthinking this way too much.  If I have the
following forwarding class using wrap_base:

struct WindowWrapper : Window, luabind::wrap_base
{
    WindowWrapper()
        : base()
    {}

    virtual void SetHeight(int h)
    {
        call<void>("SetHeight", h);
    }

    static void BaseSetHeight(Window* ptr, int h)
    {
        return ptr->Window::SetHeight(h);
    }
};


Then simply overriding SetHeight( ) in Lua will automatically work, because

win.height = 3
-- calls Window::SetHeight( )
-- which calls Lua's version of SetHeight( ), in this case
SubWindow:SetHeight( )


So as long as I maintain a consistent naming convention (property "height"
corresponds to "GetHeight" and "SetHeight"), then clients are free to
override the getters and setters in Lua.



On Mon, Feb 21, 2011 at 3:33 PM, Kitten, Nicholas
<[email protected]>wrote:

> I'll rephrase my question, with code this time:
>
> I have a C++ class, bound to Lua along these lines:
>
> luabind::class_<Window>( "Window" )
>
> .def( luabind::constructor<>( ) )
>
> .property( "height", &Window::GetHeight, &Window::SetHeight )
>
> .property( "width", &Window::GetWidth, &Window::SetWidth );
>
> /** wrap_base forwarding class omitted **/
>
>
> Of course, in Lua this means I can do the following:
>
> win = Window()
> win.width = 320        -- calls setter
> print( win.width )       -- calls getter
>
> Now, I would like to allow a client to subclass Window from within Lua,
> overriding the setters and/or getters with Lua functions, something like
> this:
>
> class 'SubWindow' (Window)
>
> function SubWindow:SetHeight( newHeight )
>
> Window.SetHeight( self, newHeight )
> --  other stuff
>
> end
>
> function SubWindow:SetWidth( newWidth )
>
>  Window.SetWidth( self, newWidth )
> --  other stuff
>
> end
>
>
> function SubWindow:__init( )
>
> Window.__init(self)
> --[[
>     magically bind derived SetHeight( ) and SetWidth( ) to __newindex
> metamethod
> --]]
>
> end
>
> win = SubWindow()
> win.width = 320        -- calls SubWindow's setter
> print( win.width )       -- calls Window's getter
>
>
> As you can see, the only way I can think to do this would be by overriding
> the __index and __newindex metamethods on the derived class, but because
> Luabind classes are userdata, this seems impossible at the moment.  I know
> the last comment I read from this list on the subject said it might possibly
> be implemented with version .9 (even though firm plans were only for 1.0) -
> has that happened?
>
> If not, is there a distinct mechanism within Luabind to override properties
> in derived classes?  I remember seeing a comment in the source saying that
> properties should "always be overridden, not overloaded", but I couldn't
> discern how the overriding would happen in the first place.
>
> Thanks,
> -Nick
>
>
>
> On Tue, Feb 8, 2011 at 12:06 PM, Kitten, Nicholas <[email protected]
> > wrote:
>
>> Does anyone know how I would go about creating a property within a
>> Lua-created class (using Lua functions for getters and setters)?  I'm
>> guessing there's support in the metatables for doing it, but I've never seen
>> an implementation.
>>
>> Thanks,
>> -Nick
>>
>
>

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